Pneumatic valves configured to be positioned within an airway and capable of opening to permit airflow and closing to obstruct airflow are well-known. When such valves close, moisture formed by condensation may become trapped between the valve plate and the interior of the airway. If the trapped moisture freezes, opening the valve may be impeded or even prevented (valve icing).
Valve icing is of concern in air turbine starter (ATS) valve assemblies used to initiate aircraft turbine engine rotation. When the ATS flow control valve is closed, condensation may be trapped between the flow control valve plate and airway's interior. This may be problematic after engine shutdown in low temperature environments (i.e. at or below freezing) because the collected water could freeze and valve icing could result. An iced ATS control valve may not open when commanded and consequently delay or prevent engine start and takeoff. Though the iced valve may be replaced or de-iced (e.g. heated), it is preferable to avoid the problem by preventing valve icing.
From the above, it should be appreciated that it would be desirable to provide a pneumatic valve assembly that minimizes the likelihood of valve icing.